The present invention is directed generally to linear voice coil actuators, and in particular to linear voice coil actuators operating as controllable electromagnetic compression springs.
A typical linear voice coil actuator 1 depicted, for example, in a one-half longitudinal cross section view in FIG. 1, consists of a field assembly 2 and a coil assembly 3. Field assembly 2 is comprised of an axially magnetized cylindrical magnet 4, soft magnetic pole piece 5 and soft magnetic housing 6. Coil assembly 3 consists of a coil 8, located in the circular cavity of the coil base 7. The coil assembly 3, when de-energized, does not have a preferred position to go to. If, on the other hand, after being de-energized, a coil has to move away from the field assembly, then some kind of feature providing repulsion force has to be present. This repulsion force is typically provided by a mechanical spring. The predictability of the characteristics of the repulsion force are therefore dependent upon and subject to the variations in mechanical characteristics of the spring. It is therefore desirable to have a linear voice coil actuator having a repulsion force which is not subject to the variations in mechanical characteristics of a mechanical spring.
The present invention provides a linear actuator that can be considered as an electromagnetic compression spring controlled by the current in coils within the actuator. When this actuator feature is employed, there is no need to use a mechanical spring to provide a repulsion force.
The present invention features a linear actuator comprising a field assembly and a coil assembly positioned for interaction with and movement relative to the field assembly, wherein the field assembly includes a soft magnetic housing, a plurality of axially magnetized cylindrical magnets positioned along an axis of and in the housing and spaced apart from one another by at least one soft magnetic pole piece, and wherein the coil assembly includes a coil base having a coil cavity and a coil positioned in the coil cavity, and an axially magnetized permanent magnet positioned on the coil base so that the axially magnetized permanent magnet is positioned to travel along the axis of the housing.
It is another feature of the present invention that a repulsion force is generated between the coil assembly and the field assembly when the coil assembly is de-energized, and the soft magnetic housing of the aforementioned field assembly has an overhang relative to the soft magnetic pole piece which affects the amount of repulsion force generated.
It is another feature of the present invention that a repulsion force is generated between the coil assembly and the field assembly when the coil assembly is de-energized, and wherein the magnitude of the repulsion force can be modified when the coil assembly is energized, and further wherein the soft magnetic housing of the aforementioned field assembly has an overhang relative to the soft magnetic pole piece which affects the magnitude of repulsion forces generated.
It is still another feature of one embodiment of the present invention that the above repulsion force supplied has a first direction when the coil assembly is energized at one level, and has a second direction, opposite the first direction, when the coil assembly is energized at a different level.
The present invention also features a linear actuator comprising a field assembly and a coil assembly positioned for interaction with and movement relative to the field assembly, wherein the field assembly includes a soft magnetic housing, a plurality of axially magnetized cylindrical magnets and a plurality of soft magnetic pole pieces which form a stack of alternating cylindrical magnets and pole pieces. The stack is positioned along an axis of and in the soft magnetic housing, so that one of the magnets is positioned against the soft magnetic base, and one of the pole pieces is located at a free end of the stack. The coil assembly includes a coil base having coil cavities, a plurality of coils supported in the coil cavity, and an axially magnetized permanent magnet positioned on the coil base so that the axially magnetized permanent magnet is positioned to travel along the axis of the soft magnetic housing.
These and other advantages and features of the present invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention and the accompanying drawings.